Large fabric buildings serve many purposes, from events to industrial project site applications. Not all fabric structures are alike, of course. Many people see a fabric building and call it a “tent”. Turns out, not all fabric buildings are tents. In fact, there are some key differences between types of fabric structures that are vitally important to the application and the users of the structure. Let’s take a look at the structural differences between traditional tents and tension fabric structures.

Differences Between Tents and Fabric Structures

We have discussed the many use differences between tent structures and fabric structures that affect how, where and how long they are in use. Tent structures tend to be best for short term use. Because of their structural design, tents may not be able to handle the stresses of different site conditions. If shelter or work space is needed longer term, months or years, then a tent may be inappropriate for that application. Because of their highly engineered structural integrity and durable materials, tension fabric structures are better suited to long-term or more demanding situations.

When selecting the appropriate product, both the client and the vendor should carefully assess the situation and make sure they have the right structure for the application. Here are some features to look for.

Structural Differences between Tents and Tension Fabric Structures.

Tents and TFS may seem to have similar designs at first glance. However, here are some key differences.

Horizontal Tensioning – A Tension Fabric Structure (TFS) uses horizontal tensioning to create a structure with integrity similar to that of a traditional steel and concrete building. With horizontal tensioning, fabric is fed into the aluminum beams of the structure’s frame, and a hydraulic ram using 10,000lbs of pressure tensions the fabric, while the horizontal frame locks the aluminum arches into place. This process incorporates the strength of the fabric into the overall strength of the structure, not just using the material as a cover as is the normal use of fabric in a tent. In contrast, tents do not horizontally tension or use the fabric to enhance the strength of the design.

Extruded aluminum beam – both structures may use this feature. The TFS has a larger beam when comparing similar size structure, making the structure stronger. The TFS generally will have larger bolts, larger cross sections, larger cables, etc. which provide a sturdy frame over which the fabric is tensioned for added strength and resistance.

Bolted Connections – TFS uses bolted connections to attach the building’s frame components together, locking them securely in place. A tent system uses hinged connections to secure the structure. Hinged connections mean a looser frame that is not as strong, rattles in the wind and is prone to leaking.

Curved vs. Straight Legs – TFS uses curved legs which add additional strength to the design and eliminates the horizontal eave which is present with straight leg tents. Curved legs and the curved profile they help provide also help the TFS to tolerate wind and rain as well as improve snowshed.

Fabric Structure Engineering and Design Make a Difference

How does a tent hold up in strong winds? Some tent vendor engineering reports state their tent can meet 100 mph wind loads. But, tents are not engineered for the long-term stresses of multiple weather events and may not be able to consistently meet such a standard for long.

Engineering for Strength and Durability

Many factors can affect the engineering of tents and tension fabric structures. One key engineering factor is MRI, or mean recurrence interval, which is a calculation that determines the wind load a building can withstand over a period of time. If the structure is needed for only a few days, the chance of a weather event is much lower than for longer periods. In that case, the possibility of weather-related structural failure, and accompanying risk and safety issues, are greatly reduced. This is why a tent company may say it meets high wind loads comparable to a fabric structure but over a longer period of time the wind load capacity would be greatly reduced.

Other key factors are occupancy, that is, what the building is being used for, and category, what type of setting the building is located in.

Generic or Custom Project Engineering

Tents are rented out repeatedly by event companies, so the engineering is typically going to be a generic configuration and installation package that fits general use and assumes only a few days of use. This generic engineering approach means a tent can fail if stressed outside that generic situation, such as a storm event.

In contrast, a tension fabric structure engineering packages is compiled specifically to meet the site and use requirements of each project, including building code, MRI, occupancy and category. The TFS is designed and installed to withstand the stresses of the site and local weather for the duration of the installation.

How to Know if it’s a Tent or a Tension Fabric Structure

What are ways a customer can determine if a rental structure is a tent?

Check the engineering report from your temporary structure rental company. Look for the MRI to see how durable the structure is in bad weather. Then check to see if the package is designed specifically for your project, adjusting for such things as intended use and location. Did your report appear immediately? If so, you probably have a tent. Because it incorporates a detailed project and site review, the configuration and installation plan of a TFS requires a typical lead time of a week to design a project-specific package.

Another indicator is where your structure comes from. Tension fabric structures are only serviced by a few expert companies, who typically will ship their highly engineered component parts across state lines to deliver your structure. Tent companies, by contrast, are in every major city, storing their structures in local warehouses. If you can find a comparable product in a nearby major city, most likely you have a tent.

Check frame size and bolt size used to connect the frame see how they compare. Are they using an extrusion? What size and how many stakes are they using to anchor the tent? Do they talk about uplift resistance, pull tests, or know what a dynamometer is to measure uplift?

Do they use horizontal tensioning (described above) on their structure or just down (vertical) tension? Very few tents use horizontal tension and this is a key differentiator.

What kind of equipment do they use to do the install? Some tents can use small forklifts and scissor lifts and others, like Allsite, will use heavy duty equipment. This might include a 10k reach forklift, a 60’ manlift, or, for larger applications, a 60 ton crane. Most tent installations are done on the ground with unskilled labor, while a good portion of the TFS installation is done in the air in man lifts with skilled installers and equipment operators.

Do you Need a Tent or a Fabric Structure?

Before you shop for a temporary structure, make sure you have a clear understanding of what your need is.

If weight needs to be supported from frame such as truss systems, fall arrest systems, etc.

For more information on the characteristics and advantages of fabric buildings, contact us to speak to one of Allsite’s fabric structure experts. We’ll be happy to help you find the perfect solution for your fabric building need.